Industrial process control systems are used to monitor and control industrial processes used to produce or transfer fluids or the like. In such systems, it is typically important to measure “process variables” such as temperatures, pressures, flow rates, and others. Process control transmitters measure such process variables and transmit information related to the measured process variable back to a central location such as a central control room.
One type of process variable transmitter is a pressure transmitter which measures process fluid pressure and provides an output related to the measured pressure. This output may be a pressure, a flow rate, a level of a process fluid, or other process variable that can be derived from the measured pressure. The pressure transmitter is configured to transmit information related to the measured pressure back to the central control room. Transmission is typically provided over a two-wire process control loop, however, other communication techniques are sometimes used.
Generally, the pressure is sensed by a pressure sensor that is coupled to the process variable transmitter and is coupled to the process fluid by some type of process coupling. In many instances, the pressure sensor is fluidically coupled to the process fluid either through an isolation fluid or by direct contact with the process fluid. The pressure of the process fluid causes a physical deformation to the pressure sensor which generates an associated electrical change in the pressure sensor such as capacitance or resistance.
In many industrial pressure measurement applications, pressure barriers are required. A pressure barrier is a mechanical structure that contains process fluid pressure in order to ensure the safety of plant personnel. As such, pressure barriers are key requirements for a process fluid pressure measurement system. In order to provide a safe and robust system, some applications require redundant pressure barriers to ensure the safety of plant personnel in the event of failure of a primary pressure barrier. Thus, if a primary barrier (such as an isolation diaphragm) fails, the process fluid is still contained by the secondary barrier (such as a glass/metal header).